A fuel supply system installed in a fuel tank is, for example, described in a patent document of JP-A-H11-101166. This fuel supply system has a cover, a pump unit and metal pipes. The cover is fastened to an opening of a fuel tank. The cover and the pump unit are connected through the use of the metal pipes, and thereby the pump unit is stored inside the fuel tank. The pump unit has a fuel pump, which is stored in a sub-tank to be installed inside the fuel tank. Moreover, the cover and the pump unit are biased by springs so as to be drawn apart each other. One end of each metal pipe is fastened to the cover and the other end thereof is movably supported by the pump unit. That is, the pump unit can be moved in the axial direction of the metal pipe relatively to the cover. Therefore, in case the inner pressure of the fuel tank is changed on the ground of the alternation of the temperature, or the amount of the fuel is changed, and thereby the fuel tank is expanded or contracted, the pump unit is biased into the bottom of the fuel tank integrally with the sub-tank by force of the springs.
The cover has cylindrical supporting portions, each of which has a though hole. The metal pipes are inserted through respective through holes, and thereby the pump unit is guided to be moved relatively to the cover. In case the metal pipes and the supporting portions are made of the same material, noisy sounds are generated when the metal pipes are moved inside the supporting portion. Therefore, the metal pipes and the supporting portions are respectively made of different materials, and thereby the noisy sounds are restricted to be generated.
However, for example, when the metal pipes are made of metal, the solidity of which is high, and the supporting portions are made of resin, the solidity of which is low, sliding resistances between the metal pipes and the supporting portions are disadvantageously heightened. When the sliding resistances are heightened, the pump unit cannot be moved in accordance with the expansion and the contraction of the fuel tank. Accordingly, fuel suctioning performance of the fuel supply system is likely to be lowered.
It is considered that the surfaces of the metal pipes are advantageously processed. However, depending on the shape of the fuel tank, or depending on the expansion or the contraction of the fuel tank, the axes of the metal pipes are not always disposed perpendicularly to an inner bottom surface of the fuel tank. When the metal pipe is not perpendicular to the inner bottom surface of the fuel tank, the metal pipe is declined inside the supporting portion, and thereby only some parts of the metal pipe contact some parts of the supporting portion forcefully. In this case, even though the surface of the metal pipe is advantageously processed, the sliding resistance between the metal pipe and the supporting portion increases.
For example, as shown in FIG. 8, when a part of a metal pipe 101 contacts a supporting portion 100 around its upper end 100a, the other part of the metal pipe 101 contacts the supporting portion 100 around its lower end 100b. Since these contacting areas of the metal pipe 101 and the supporting portion 100 are small, loads are concentrated on the contacting areas. Therefore, the metal pipe 101 cannot be smoothly moved inside the supporting portion 100, that is, the pump unit cannot be smoothly moved relatively to the cover.